PROJECT SUMMARY Over the past ~5 years, we have examined the role of MeCP2 in neurotransmission as a transcriptional factor impacting gene expression. Our data has revealed that MeCP2 is a bona fide regulator of synaptic function with bidirectional changes in MeCP2 resulting in reciprocal alterations in neurotransmission. We have also shown alterations in MeCP2 expression in mice result in several behavioral phenotypes as well as deficits in specific measures of synaptic plasticity further implicating MeCP2 as a key mediator of synaptic processes. A rather surprising finding in the field of depression has been the demonstration that scopolamine, a muscarinic acetylcholine receptor antagonist, has rapid and long-lasting antidepressant responses in depressed individuals. We have started to investigate the mechanism of the antidepressant action of scopolamine, and have found it is dependent on MeCP2 expression as these effects are lost in Mecp2 knockout mice. Our findings also suggest that the antidepressant effects of scopolamine are dependent on MeCP2-dependent transcriptional mechanisms resulting in increased BDNF expression that is important for the behavioral effects. Our preliminary data further suggests that scopolamine triggers MeCP2 phosphorylation at Serine 421 (pMeCP2), which has been shown to regulate BDNF expression. In initial experiments, we find that scopolamine acts via blockade of the muscarinic M1 receptor to trigger pMeCP2. The objective of this grant is to explore the novel hypothesis that MeCP2- dependent transcriptional mechanisms underlie the fast acting antidepressant effects of scopolamine. We will use state of the art behavioral as well as cellular and biochemical approaches to examine our hypothesis. Collectively, these studies will contribute to a better understanding of mechanisms underlying fast-acting antidepressant responses as well as provide novel insight into MeCP2 regulation as a therapeutic target.